1. Field of the Invention
The present invention relates to a new catalyst, a process for preparing the catalyst and processes for the dehydrogenation of dehydrogenatable C.sub.2-30 hydrocarbons, preferably C.sub.2-5 paraffins, using the new catalyst.
2. Description of the Invention Background
The dehydrogenation of paraffins to olefins is of considerable commercial importance due to the need for olefins for the manufacture of products such as high octane gasolines, synthetic elastomers, detergents, plastics, ion exchange resins and pharmaceutical products. For a dehydrogenation process to be commercially useful, it must utilize catalysts exhibiting a high activity, a high rate of conversion, a high selectivity for the formation of olefins, and a high stability.
A large number of catalysts are previously known for the dehydrogenation of paraffins. These catalysts comprise a solid carrier material on an inorganic oxide basis and various catalytic metals and promoter metals deposited on the carrier material or incorporated into the carrier material by other means. Carrier materials on an alumina basis have been widely used in such dehydrogenation catalysts.
U.S. Pat. No. 4,788,371 discloses such catalyst and a process for the steam dehydrogenation of dehydrogenatable hydrocarbons with oxidative reheating. A dehydrogenatable C.sub.2-30 hydrocarbon, steam and an oxygen-containing gas are contacted in a reaction zone with a catalyst comprising a Group VIII noble metal, one or more components selected from lithium, potassium, rubidium, cesium and francium, and a component selected from boron, gallium, indium, germanium, tin and lead, deposited on an inorganic oxide carrier material. The preferred carrier material is alumina having a surface area of 1-500 m.sup.2 /g, preferably 5-120 m.sup.2 /g. Alumina is employed as the catalyst carrier in all the working examples of the patent. A preferred catalyst according to said U.S. patent contains about 0.70 wt. % of platinum, about 0.50 wt. % of tin and about 3.86 wt. % of cesium, and has a surface area of about 85 m.sup.2 /g.
Mixtures of magnesium oxide MgO and alumina Al.sub.2 O.sub.3 and mixed oxides of Mg and Al have also been utilized as catalysts, and as carrier materials for catalysts. International Patent Application No. PCT/JP89/00053 discloses an alkoxylation catalyst comprising a magnesium oxide that has been modified by adding thereto at least one trivalent metal ion, preferably selected from Al.sup.3+ and Ga.sup.3+. British Patent Application GB 2,225,731 discloses a catalyst for hydrotreatment, e.g. hydrodemetallization or hydrodesulphurization, comprising in a substantially homogenous phase magnesia and alumina wherein the molar ratio of Mg to Al is preferably from 3:1 to 10:1, together with a Group VI metal and/or at least one Group VIII metal.